Confirmation numbers are given out so that if there is ever a problem with your purchase, they can pull up the transaction on their end. It's simply an identifier for the transaction. If they ever need to validate that it is truly your purchase, they will ask for the confirmation number. You don't need to do anything, just pull up the ticket when you get to the theatre and let them scan it off your phone. You should be able to add it to your Apple Wallet if you use that (makes it easy).